The present invention is directed to cap assemblies for sealing thin walled test tubes in ultra high speed vertical tube rotor centrifuges. More particularly, the invention is directed to a test tube cap assembly having no central aperture within the cap assembly for insertion or removal of fluid sample being subjected to centrifugation.
As set forth in our concurrently filed patent application Ser. No. 788,484 filed Apr. 18, 1977, entitled A TUBE CAP FOR PREPARATIVE CENTRIFUGE ROTORS, the present test tube cap assembly utilizes the tapered or frustoconical shaped bushing or sealing means for use with the cap assembly. as stated in the above referenced copending patent application, the design of the cap assembly is conducive for use with rotors wherein the hydraulic pressures which are exerted on the tube cap assembly by the liquid within the test tube increase the sealing force of the cap assembly. Consequently, the increased forces placed upon the cap assembly are automatically accommodated by the increased sealing in the cap assembly.
However, in prior cap assemblies a central aperture or channel has been used for the insertion or removal of fluid sample within the test tube. During centrifugation a filler screw is placed within the channel to prevent leakage. However, during high speed centrifugation with a vertical or nearly vertical tube rotor, this central aperture is susceptible to leakage caused by the centrifugation pressures from within the test tube exerted by the fluid sample. The sealing arrangement, as set forth in our copending patent application, is directed primarily to gripping the upper portion of the test tube within the crown member of the cap assembly.
Therefore, it is necessary as a unique problem with respect to vertical or nearly vertical tube rotors to design the cap assembly without the central aperture and yet permit easy removal of the cap assembly with minimum disturbance of the tube contents. The primary purpose for an aperture in the cap assembly is to allow access to within the test tube for removal of the centrifuged sample before actual removal of the cap assembly. Hence, the tube is disturbed as little as possible prior to removal of the centrifuged sample. The practice has been to remove the filler screw in the cap assembly and to allow retrieval of the sample. In some applications it is impractical to extract the tube contents through a small aperture in the cap. Rather, it is desirable to be able to remove the entire cap without disturbing the liquid contents.
If the central aperture is eliminated, it is necessary to remove the complete cap assembly prior to removal of the sample within the test tube. Typically, as shown in our above referenced copending application, the operation of the sealing mechanism utilizes a nut which is tightly secured to an upper end of a stem. The use of such a configuration would undoubtedly result in an undesired disturbance to the test tube centrifugated sample because, after the nut is loosened, the stem would then have to be pushed down into the tube somewhat to break the seal.
Consequently, a need arises with respect to having a cap assembly which does not have a central aperture, but provides an easy removal after centrifugation without disturbing the centrifuged liquid within the test tube.